1. Field of the Invention
The present invention relates to compounds that absorb ultraviolet light 380 nm to 400 nm range while avoiding absorption in the yellow light range, i.e., 410-420 nm having suitable refractive characteristics useful in the preparation of optical resins or plastics suitable, for example, for the manufacture of ophthalmic lenses.
The present invention is also directed to methods of making these compounds, polymeric blends containing such compounds, optical devices containing the compounds, and methods for preparing these optical devices.
2. Description of Related Art
In recent years, transparent synthetic resins have found increasing applications as optical plastic materials replacing inorganic optical materials because of their light weight and good impact strength, moldability or processability and dyeability.
Plastics used in the preparation of optical devices must have properties suitable for the intended purpose. These materials should, inter alia, be transparent, non-yellowing, and have a suitable refractive index. In general, the higher the refractive index polymer allows for a thinner more lightweight lens, as well as an improved physical appearance. A refractive index of 1.5 or greater is desired, and higher refractive index plastics, e.g., 1.6, 1.7, 1.8 or more, are preferred.
The dangers of ultraviolet light to eyes is well-documented. Therefore, there have been many attempts to make and commercialize optical plastic materials that filter out ultraviolet light. Many such attempts have involved the incorporation of compounds that absorb ultraviolet light into the plastic material.
Ultraviolet absorbent plastics are well-know in the art. For example, U.S. Pat. No. 5,298,189 to Kauffman describes proton transfer, bis-benzoxazole, fluorescent compounds, i.e., fluors that include substituted or unsubstituted 1,4-bis(2-benzoxazolyl)-2-hydroxybenzenes and 1,4-bis(2-benzoxazolyl)-2-amidobenzenes that absorb ultraviolet light in the 300-420 nm range and fluoresce in the 480 to 560 nm range. These are said to be useful in organic scintillator systems.
U.S. Pat. No. 5,587,112 to Kauffman et al. discloses a class of proton transfer, 2-benzoxazolyl moieties covalently bound to an aromatic fused ring heterocyclic moiety. These compounds absorb ultraviolet light in the 420 nm or shorter, e.g., 300 to 420 nm range, and fluoresce in the 520 nm to 800 nm range. These compounds are said to be useful in the manufacture of fluorescent coatings, objects, scintillators, light sources and the like.
However, such previous ultraviolet absorbers have a propensity towards absorbing yellow light in the 410 to 420 nm range, which leads to a yellow color of a lens containing such absorbers. To obtain maximum ultraviolet absorption while avoiding yellowing, a lens should absorb ultraviolet light in the 380 nm to 400 nm range while avoiding absorption in the yellow light range, i.e., 410 to 420 nm. However, obtaining such a sharp “cut” or reduction on the absorbance ability of an ultraviolet absorber in such a narrow range has not proven easy, and ultraviolet absorbers exhibiting the preferred ultraviolet absorption in the 380 to 400 nm range without absorption in the 410 to 420 nm range are not taught or suggested in the aforementioned patents.
New polymers having such absorption qualities are desirable for use as, inter alia optical lenses, as these would avoid undesirable yellowing.